Glucose comes from the breakdown of food. It is the body's energy source. It can pass from the blood to cells with a hormone called insulin. Without insulin, glucose will build up in the blood. This is called hyperglycemia. At the same time, your body's cells are starved for glucose (energy).
When this happens during pregnancy it is called gestational diabetes. The extra glucose in the blood can cross to the baby. This condition can cause problems for the mother and baby.